A protein deamidase is an enzyme that hydrolyzes amide groups of glutamine and asparagine in a protein to convert to glutamic acid and asparaginic acid and isolates ammonia. A protein deamidase is applicable to various uses such as improvement in functionalities of a protein (solubility, emulsification characteristics, foam characteristics, gelation characteristics, etc.), improvement in extension of dough of wheat gluten, reduction of wheat allergen induction, improvement in efficiency of protein extraction from agricultural products, and improvement in calcium solubility in a protein solution, and is an enzyme having high industrial applicability.
Protein deamidases exist widely in the natural world. As the most known protein deamidase, a protein-glutaminase derived from a microorganism is exemplified (Patent documents 1 and 2). As a protein deamidase derived from plants, existence of an enzyme that deamidates a glutamine residue in a protein from wheat in germination, kidney beans, pumpkin seeds has been reported (Non-patent document 1). Existence of protein deamidases has been widely known in the natural world including living organisms as well, and, for example, a transglutaminase derived from actinomyces that has been broadly used as an enzyme for food processing in recent years catalyzes a crosslinking reaction between a glutamine residue and a lysine residue in a protein, but deamidates a glutamine residue in a protein when primary amine such as lysine is not present in a reaction system (Non-patent document 2). Existence of a peptide glutaminase that is an enzyme deamidating a glutamine residue in a peptide in a fungus body of a bacterium (Bacillus circulans) has been reported for other microorganisms (Non-patent document 3).
When a protein deamidase is used, a substrate and a concentration of an enzyme, a reaction temperature, a reaction time, and the like are adjusted according to its application in the same manner as the other enzymes. However, only adjustment of such enzyme reaction conditions may cause the case that a desired product cannot be produced or the case that an expected yield cannot be obtained, and thus, the requirement of modifying properties of a protein deamidase has arisen. Furthermore, although preservation stability is important when a protein deamidase is used as an industrial enzyme preparation, an enzyme is generally low in stability to oxygen, and thus, addition of a stabilizing agent or wrapping in a degassed state is required to maintain sufficient preservation stability, which has led to cost increase.
In order to modify properties of a protein deamidase, in general, it is necessary that a mutant of a protein deamidase is prepared, and its activity, substrate specificity, and the like are evaluated to identify an excellent mutant, but these processes required a large amount of labor.    Patent document 1: Japanese Patent Application Laid-Open (JP-A) No. 2000-50887    Patent document 2: JP-A No. 2001-218590    Patent document 3: JP-A No. 2004-97099    Non-patent document 1: Vaintraub, Kotova, L. V. & Shaha, R. (1996) Protein deamidases from germinating seeds. Physiol. Plantarum. 96, 662-666    Non-patent document 2: “Industrial Enzymes” (1995) Takayuki Uwajima, MARUZEN CO., LTD., 3.2.6 Modification of food functions “Use of transglutaminase” pp. 40-42    Non-patent document 3: Kikuchi, M., Hayashida, H., Nakano, E. & Sakaguchi K. (1971) Peptidoglutaminase. Enzymes for selective deamidation of γ-amido of peptide-bound glutamine. Biochemistry 10, 1222-1229